Onion — Food safety facts
Do not feed · Dogs · full breakdown on the linked food page
Toxic. Damages red blood cells (hemolytic anemia). Powdered onion is concentrated. Danger can appear 1–5 days later.
Short answer
Yes, onion powder is highly toxic for dogs. It's a concentrated form that can damage their red blood cells, leading to anemia. Symptoms like weakness or pale gums may not show up for a few days. Call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 right away.